1. Field of the Invention
The present invention generally relates to a communication system, and more particularly to a method and apparatus for selectively transmitting images in a mobile communication system.
2. Background of the Related Art
Video telephony is one of many services provided by third-generation mobile communication terminals. Video telephony is a circuit-switched service in which image and voice information is simultaneously transmitted after a bearer is set at a fixed rate. Through this service, the calling party can execute a call while viewing an image of the called party.
In implementing video telephony in a mobile terminal, both voice data of the user and image data input through a camera are transmitted. The transmission ratio of this data follows the transmission rate required by the network.
FIG. 1 shows a video telephony apparatus included in a mobile terminal. A signal flow through this apparatus is also shown. The apparatus includes an input selector 10 for inputting an image signal and a voice signal from a camera (not shown) and microphone (not shown) respectively, a video codec unit 20 for coding the image signal, an audio codec unit 30 for coding the voice signal, and a multiplexer 40 for mixing the coded image signal and voice signal. The apparatus also includes a radio communication unit 50 for transmitting an output signal of the multiplexer 40 to a network 200, and a controller 60 for controlling general operations of the elements used to transmit the image signal and voice signal.
The video telephony apparatus operates as follows. An image signal input through an internal or external camera of the terminal and a voice signal input through a microphone (not shown) are respectively coded to a transmittable form, mixed in the multiplexer, and then transmitted to the wireless network through the radio communication unit.
The signal flow shown in FIG. 1 is a general signal flow set at such a rate that a transmitter in the network could transmit both an image and voice. That is, the input selector selects and inputs both an image signal and voice signal. The input image signal is coded into a signal to be transmitted through the video codec unit, and the voice signal is coded into a signal to be transmitted through the audio codec unit. The coded signals are then mixed in the multiplexer unit under control of the controller. The mixed signal is then transmitted to the wireless network through the radio communication unit, and the wireless network transmits the corresponding signal to a receiver's mobile communication terminal, where the receiver can simultaneously check the image and voice provided from the transmitter.
Because traffic in the network continuously changes, an image may not always be able to be transmitted. This is true especially if the network is set at a low transmission rate. For example, if the wireless network environment is not good, some image frames transmitted as frame data may be lost and thus a broken image will be received. The image frames transmitted as frame data may correspond to a moving picture derived from a terminal camera. Also, if network conditions are not good, still images may be irregularly transmitted or only voice signals may be transmitted regardless of the type of signals transmitted from the transmitter.
The aforementioned video telephony method therefore has at least the following problems. Since image data within a frame structure is transmitted in spite of a bad transmission environment of the network, the image data may be partially lost and thus a broken image may be received. Or, a still image that the user does not intend to send may be transmitted. Also, if the transmission rate of the network is set to a lowest value, only voice signals can be transmitted. This eliminates or at least diminishes the ability to provided video telephony services in a mobile terminal.